Ag-sheathed tapes produced with prereacted Bi2223 powder: critical currents and impurity phase development

We have performed investigations of phase coexistence and critical current density on tapes of (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O x (2223) with a silver sheath, produced by the powder-in-tube method. The powder used was prereacted 2223 phase (with mainly 2212 impurities). It was found that the 2201 phase is formed (and the 2212 phase disappears) at 840 degrees C in an Ag sheath, indicating that a different phase equilibrium may exist with and without the Ag sheath. Post-annealing at T<830 degrees C leads to a reappearance of the 2212 phase while the 2201 phase disappears. Transport critical current densities (77 K, self-field) are zero for tapes quenched from 840 degrees C. For tapes post-annealed at lower temperatures it appears as if all of the current is carried in links of 2212 (and not 2223) created between 2223 grains.